First, a variety of mobile communication systems applicable to the present invention will hereinafter be described in detail.
A Universal Mobile Telecommunications System (UMTS) network configuration applicable to the present invention will be described below.
FIG. 1 illustrates a UMTS network configuration.
Referring to FIG. 1, a UMTS system includes a User Equipment (UE), a UMTS Terrestrial Radio Access Network (UTRAN), and a Core Network (CN). The UTRAN includes one or more Radio Network Sub-systems (RNSs) each having a Radio Network Controller (RNC) and one or more base stations (Node Bs) managed by the RNC. One or more cells may exist per a single base station (Node B).
A radio protocol architecture for the UMTS will be described with reference to FIG. 2. FIG. 2 illustrates a radio protocol architecture for UMTS. Pairs of radio protocol layers exist in the UE and the UTRAN, and perform data transfer over an air interface. In the radio protocol layers, a physical (PHY) layer, which is a first layer (L1), is responsible for data transfer over an air interface using various radio transfer technologies. The PHY layer is connected to a medium access control (MAC) layer, which is a higher layer, through a transport channel, and the transport channel is divided into a dedicated transport channel and a common transport channel depending on whether or not the channel is shared.
A MAC layer, a radio link control (RLC) layer and a broadcast and multicast control (BMC) layer exist in a second layer (L2). The MAC layer maps various logical channels to various transport channels and performs logical channel multiplexing to map a plurality of logical channels to one transport channel. The MAC layer is connected to the RLC layer, which is a higher layer, through a logical channel. The logical channel is divided into a control channel for transmitting information on a control plane and a traffic channel for transmitting information on a user plane, according to the kind of transmitted information.
In addition, the MAC layer is divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs/ehs sublayer, and a MAC-e/es or a MAC-i/is sublayer, according to the kind of the managed transport channel. The MAC-b sublayer is responsible for management of a Broadcast Channel (BCH) which is a transport channel for broadcasting system information, the MAC-c/sh sublayer is responsible for management of a Forward Access Channel (FACH) common transport channel shared with the other UEs, and the MAC-d sublayer is responsible for management of either a Dedicated Channel which is a dedicated transport channel of a specific UE or a Dedicated Enhanced Dedicated Channel (Dedicated E-DCH). In addition, the MAC-hs/ehs sublayer manages a High Speed Downlink Shared Channel (HS-DSCH) for high-speed downlink data transmission and the MAC-e/es or MAC-i/is sublayer manages an Enhanced Dedicated Channel (E-DCH) which is a transport channel for high-speed uplink data transmission.
The RLC layer ensures the Quality of Service (QoS) of Radio Bearers (RBs) and is responsible for data transmission. The RLC layer has one or two independent RLC entities for each RB in order to ensure QoS. To support various QoS levels, the RLC layer provides three RLC modes, Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). In addition, the RLC layer controls a data size to suit radio data transmission at a lower layer. For controlling a data size, the RLC layer segments or concatenates data received from a higher layer.
The PDCP layer is located above the RLC layer. The PDCP layer enables efficient data transmission in IP packets such as IP version 4 (IPv4) or IP version 6 (IPv6) packets on a radio link having a relatively narrow bandwidth. For this purpose, the PDCP layer performs header compression. Since only necessary information is transmitted in the header of data header through header compression, the transmission efficiency of the radio link is increased. The PDCP layer exists mainly in a Packet Switched (PS) domain because header compression is it basic function. To provide an efficient header compression function for each PS service, one PDCP entity is defined for each RB. However, if the PDCP layer exists in a Circuit Switched (CS) domain, the PDCP layer does not provide the header compression function.
In the second layer, a Broadcast/Multicast Control (BMC) layer is located at a level above the RLC layer so as to perform a function for scheduling a cell broadcast message and broadcasting the cell broadcast message to UEs located in a specific cell.
A Radio Resource Control (RRC) layer located at the lowermost level of the third layer (L3) is defined only in the control plane and is responsible for control of the parameters of the first layer and the second layer in association with configuration, re-configuration and release of Radio Bearers (RBs), and is responsible for control of the logical, transport and physical channels. The RB is a logical path that the first and second layers of the radio protocol provide for data communication between the UE and the UTRAN. Generally, Radio Bearer (RB) configuration means that a radio protocol layer necessary to provide a specific service and channel characteristics are defined and their detailed parameters and operation methods are configured.
A Non Access Stratum (NAS) layer located at a higher level of the third layer (L3) includes a Mobility Management (MM) entity and a Connection Management (CM) entity. The MM entity performs a Temporary Mobile Subscriber Identity (TMSI) reordering process, an authentication process, a UE identification process, an International Mobile Subscriber Identity (IMSI) appending process, etc., identifies each UE, and manages several UEs. In addition, the MM entity manages current location information of a UE through a location information updating process. The CM entity provides and controls a service provided by a network. Accordingly, the CM entity performs connection establishment, management and termination of a voice call, connection establishment, management and termination of session corresponding to data communication and provision and control of a Short Message Service (SMS), or connection establishment, management and termination of a supplementary service.
The RRC and NAS messages are transmitted through a logical path called a signaling radio bearer (SRB). SRB#0 is used to transmit all RRC messages transmitted through a CCCH logical channel. SRB#1, SRB#2, SRB#3, SRB#4 are used to transmit all RRC or NAS messages transmitted through a DCCH logical channel. SRB#1 and SRB#2 are used to transmit the RRC message, and SRB#3 and SRB#4 are used to transmit the NAS message.
Next, a Long Term Evolution (LTE) system applicable to the present invention will hereinafter be described below.
The LTE system has evolved from a legacy UMTS, basic standardization thereof is now being conducted by the 3rd Generation Partnership Project (3GPP), and a representative LTE system structure thereof is shown in FIG. 3.
FIG. 3 is a conceptual diagram illustrating an LTE system.
Referring to FIG. 3, the LTE system can be generally classified into an Evolved UMTS (E-UTRAN) and an Evolved Packet Core (EPC). The E-UTRAN includes a UE and an Evolved Node-B (eNB). An interface between a UE and an eNB is referred to as a Uu interface, and an interface between eNBs is referred to as an X2 interface.
The EPC may include a mobility management entity (MME) and a serving gateway (S-GW). An interface between an eNB and an MME is referred to as S1-MME interface, and an interface between an eNB and an S-GW is referred to as an S-U interface, and a generic term of the two interfaces may also be called an S1 interface.
A radio interface protocol is defined in the Uu interface acting as an air interface. The radio interface protocol includes a physical layer, a data link layer, and a network layer in a horizontal direction. In a vertical direction, the radio interface protocol includes a user plane for transmitting data information and a control plane for transmitting a control signal (i.e., a signaling message). The protocol layers shown in FIG. 3 may be classified into a first layer (L1) including a physical (PHY) layer, a second layer (L2) including MAC/RLC/PDCP layers, and a third layer (L3) including the RRC layer on the basis of the three lower layers of an Open System Interconnection (OSI) reference model well known in the field of communication systems. The UE and the E-UTRAN include a pair of such radio protocol layers, and are used to transmit data via an air interface.
FIGS. 4 and 5 illustrate a control plane and a user plane (U-Plane) of the LTE system radio protocol.
Functions of individual layers will hereinafter be described with reference to FIGS. 4 and 5.
A physical (PHY) layer serving as the first layer (L1) transmits an information transfer service to a higher layer over a physical channel. The physical (PHY) layer is connected to a Medium Access Control (MAC) layer serving as a higher layer over a transport channel. Through the transport channel, data is transferred from the MAC layer to the physical layer or is also transferred from the physical layer to the MAC layer. In this case, the transport channel is largely classified into a dedicated transport channel and a common transport channel depending on whether or not the channel is shared. In addition, data is transferred between different PHY layers (i.e., between a PHY layer of a transmitter and a PHY layer of a receiver) over a physical channel using radio resources.
A variety of layers exist in the second layer (L2). The MAC layer maps various logical channels to various transport channels and performs logical channel multiplexing to map a plurality of logical channels to one transport channel. The MAC layer is connected to the RLC layer, which is a higher layer, through a logical channel. The logical channel is divided into a control channel for transmitting information on a control plane and a traffic channel for transmitting information on a user plane, according to the kind of transmitted information.
The radio link control (RLC) layer of the L2 layer segments and concatenates data received from a higher layer, such that it controls a data size to suit radio data transmission at a lower layer. For controlling a data size, the RLC layer segments or concatenates data received from a higher layer. To support various QoS levels requisite for various radio bearers (RBs), the RLC layer provides three RLC modes, Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). Specifically, an AM RLC performs a retransmission function using an Automatic Repeat and Request (ARQ) function so as to implement reliable data transmission.
The packet data convergence protocol (PDCP) layer of the L2 layer enables efficient data transmission in IP packets such as IP version 4 (IPv4) or IP version 6 (IPv6) packets on a radio link having a relatively narrow bandwidth. For this purpose, the PDCP layer performs header compression to reduce the size of an IP packet header including relatively large and unnecessary control information. Since only necessary information is transmitted in the header of data header through header compression, the transmission efficiency of the radio link is increased. In addition, in the LTE system, the PDCP layer performs a security function, this security function is composed of a ciphering function (also called an encryption function) for preventing a third party from eavesdropping data and an integrity protection function for preventing a third party from handling data.
In the LTE system, the ciphering, deciphering and integrity check are performed in the PDCP layer, such that the LTE system may have an input parameter value different from that of the UMTS.
The Radio Resource Control (RRC) layer located at the top of the third layer (L3) is defined only in the control plane and is responsible for control of logical, transport, and physical channels in association with configuration, reconfiguration and release of Radio Bearers (RBs). The RB is a logical path that the first and second layers (L1 and L2) provide for data communication between the UE and the UTRAN. Generally, Radio Bearer (RB) configuration means that a radio protocol layer needed for providing a specific service, and channel characteristics are defined and their detailed parameters and operation methods are configured. The Radio Bearer (RB) is classified into a Signaling RB (SRB) and a Data RB (DRB). The SRB is used as a transmission passage of RRC messages in the C-plane, and the DRB is used as a transmission passage of user data in the U-plane.
FIG. 6 illustrates a bearer service structure for use in the LTE system.
Referring to FIG. 6, the RB is a bearer provided in the Uu interface so as to support a user service. The 3GPP system has defined bearers of individual interfaces, and has guaranteed independency between interfaces. In more detail, a generic term of bearers provided by the LTE system is an Evolved Packet System (EPS) bearer, and the EPS bearer is classified into a radio bearer (RB) and an S1 bearer for each interface as shown in FIG. 6.
In FIG. 6, a Packet Gateway (P-GW) is a network node for connecting an LTE network to another network, and an EPS bearer provided by the LTE system is defined between a UE and a P-GW. The EPS bearer is further segmented between respective nodes of the LTE system, a bearer between a UE and an eNB is defined as a radio bearer (RB), a bearer between an eNB and an S-GW is defined as an S1 bearer, and a bearer between internal S-GW and P-GW of the EPC is defined as an S5/S8 bearer. Each bearer is defined as a QoS. In this case, the QoS includes a data rate, an error rate, a delay, etc. Accordingly, provided that a QoS to be provided by the LTE system is defined as an EPS bearer, different QoSs are assigned to individual interfaces, and each interface may establish a bearer in response to its unique QoS. Bearers of individual interfaces are designed to divisionally provide individual parts of a QoS of the entire EPS bearer. The EPS bearer, other radio bearers, the S1 bearer, etc. are connected in a one to one basis.
Next, the Long Term Evolution Advanced (LTE-A) system applicable to the present invention will hereinafter be described below.
The LTE-A system has evolved from the LTE system according to the IMT-advanced condition acting as the fourth-generation mobile communication condition recommended by the International Telecommunication Union-Radiocommunication sector (ITU-R), the LTE-A system standardization is now being conducted in the 3GPP that has developed the current LTE system standard.
Representative technologies newly added to the LTE-A system may include a carrier aggregation (CA) technology that extends or flexibly utilizes a bandwidth, a relay technology for increasing coverage, supporting group mobility, and enabling UE-purposed network arrangement, etc.
The relay is used as an intermediary in data between a UE and an eNB. In the LTE system, if the UE is very far from the eNB, communication is not smoothly performed. In order to overcome the above-mentioned problem, the relay has been introduced to the LTE-A system. In order to perform the above-mentioned relay function, a new network node known as a relay node (RN) has been introduced between a UE and an eNB. In this case, the eNB configured to manage the RN is referred to as a donor eNB (DeNB). In addition, the interface between an RN and a DeNB is defined as an Un interface, differently from the Uu interface acting as the interface between a UE and a network node.
FIG. 7 is a conceptual diagram illustrating the relay node (RN) discussed in the LTE-A system and the Un interface.
Referring to FIG. 7, the RN manages a UE on behalf of a donor eNB (DeNB). In other words, from the viewpoint of the UE, the RN operates as a DeNB. Accordingly, MAC/RLC/PDCP/RRC acting as the Uu interface protocols used in the legacy LTE system may be used in the Uu interface between the UE and the RN without any change.
From the viewpoint of the DeNB, the RN may operate as a UE or an eNB according to conditions. That is, when the relay node initially gains access to the DeNB, since the DeNB is not aware of the presence of the RN, the RN can access the DeNB through random access in the same manner as in the UE. After the RN has accessed the DeNB, the RN operates in the same manner as the eNB that manages the UE connected to the RN itself. Therefore, the Un interface protocol needs to be defined as the sum of the Uu interface protocol function and the network protocol function. Presently, the 3GPP has discussed, in association with the Un protocol, information as to which function must be added to or changed in each protocol layer on the basis of the Uu protocol such as MAC/RLC/PDCP/RRC.